In a projection optical system of the related art, when a lens is reduced, an efficiency may be degraded due to a ray which is not incident onto the lens but is leaked. The leaked light may be focused in an unintentional location, which may act as an obstruction from the point of view of a design or regulations. A current design trend of the head lamp is to implement a small-sized optical module and a thin and elongated head lamp.
However, when a thin aspherical lens is applied, a beam pattern as illustrated in FIG. 1 is formed due to light which is leaked outside the lens. Circular light which is illustrated at the center of FIG. 1 is focused light and semicircular light which is above and below the focused light is leaked light. Here, the thin aspherical lens refers to a lens in which a width in a vertical direction are smaller than that of a general semicircular lens due to upper and lower cut surfaces. In order to prevent the light from being leaked, as illustrated in FIG. 2, a target beam pattern having a width of 30 degrees needs to be set. That is, a required hot zone and a luminous intensity are selected using a primary optic to design the head lamp therefor.
In the meantime, as an example of an optic structure, Korean Patent Registration No. 1230132 discloses a head lamp for a vehicle in which a chemical machining process is performed on a rear surface of an optic processing unit to uniformly emit light from one LED onto the entire optic processing unit.